With reference to FIG. 11 for the structure of a conventional lamp tube socket 91, the conventional lamp tube socket 91 has a longitudinal plug hole 910, and a metal clip 911 installed in the plug hole 911. To install a lamp tube 92, a terminal 920 at an end of the lamp tube 92 is plugged longitudinally into the plug hole 910 of the lamp tube socket 91, so that the terminal 920 is contained in the plug hole 910 of the lamp tube socket 91, and then the lamp tube 92 is turned to rotate the terminal 920 by 90 degrees, so that the terminal 920 is clamped by and electrically coupled to the metal clip 911 to achieve the effects of connecting to a power supply and positioning the lamp tube 92.
When there is an earthquake, the lamp tube 92 may be shaken transversally, and the terminal 920 of the lamp tube 92 may slide and separate from the clamp of the metal clip 91, since the terminal 920 of the lamp tube 92 is clamped sideway by the metal clip 911 only. Thus, the lamp tube 92 may fall out and cause accidents.